Carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx) and the like are included in exhaust gas from an automobile engine. Furthermore, particulate matter such as tin and the like are included in the exhaust gas discharged from diesel engines, and exhaust gas cleaning systems that use a ceramic catalytic converter or a diesel particulate filter (DPF) are known as methods for removing these particles. For example, a ceramic catalytic converter basically includes a metal casing and a honeycomb shaped ceramic catalyst carrier, for example, housed therein.
A standard form of a ceramic catalytic converter includes a catalyst carrier, casing for housing the carrier, and insulation material that is packed in gaps between the outer circumferential surface of the catalyst carrier and the inner surface of the casing. The insulation material holds the catalyst carrier, and prevents mechanical shock due to impact, vibration, or the like from being inadvertently applied to the catalyst carrier. Thereby, damage and movement of the catalyst carrier can be sufficiently suppressed, and therefore the desired effect can be achieved for a long period of time. This type of insulation material has a function of holding a pollution control element such as the catalyst carrier or the like, and therefore is generally also referred to as a retaining material.
Japanese Unexamined Patent Application 2012-157809 discloses a retaining material containing a mat made from inorganic fiber material and an aggregate containing an organic binder and inorganic particles, the aggregate thereof being impregnated into essentially the entire mat. Japanese PCT Patent Application 2009-508044 discloses a retaining material containing an inorganic fiber material mat and at least one friction layer that includes inorganic colloid particles. Japanese Unexamined Patent Application 2013-127244 discloses a retaining sealing material where an inorganic binder and an organic binder are attached to a mat with a predetermined thickness.